Qilu Evening News·Qilu One Point reporter Zhao Bo
On October 2, at a depth of 105 meters below the sea level in Jiaozhou Bay, as the “Guo Signal” shield machine cutterhead reached the dividing mileage, the Qingdao Jiaozhou Bay Second Tunnel Service Tunnel, invested and constructed by Qingdao Guoxin Group and constructed by China Railway 14th Bureau, completed the shield excavation task, marking the completion of the shield excavation of the world’s longest submarine highway tunnel. After the completion of the project, it will work with the existing Jiaozhou Bay Tunnel, Jiaozhou Bay Cross-sea Bridge, and Bay-Ring Expressway to build a multi-level cross-bay comprehensive transportation network, promoting Qingdao to officially enter the “double-tunnel era.”
Qingdao Jiaozhou Bay Second Tunnel Project has a total length of 17.48 kilometers, and the main body of the tunnel is 14.37 kilometers long. It is based on the layout of “dual main tunnels + intermediate service tunnels”, with six lanes in both directions, and a design speed of 80 kilometers per hour. According to the different geological conditions of the Jiaozhou Bay sea area, the project adopts the “drilling and blasting + shield tunneling” combined construction method, excavating from the east and west sides of Jiaozhou Bay to Jiaozhou Bay, and docking in the sea. The shield section uses two super-large-diameter shield machines with a diameter of 15.63 meters and a shield machine with a diameter of 8.18 meters for excavation construction. The China Railway 14th Bureau is responsible for the shield excavation tasks of the 3,255-meter south line main line tunnel and the 5,855-meter intermediate service tunnel, using “Haitian” and “Guoxiang” shield machines for construction respectively.
On the morning of October 1, the reporter followed the construction workers of China Railway 14th Bureau into the service tunnel. The tunnel construction was busy and the workers were changing the blades of the shield machine. Zhao Zhenning, deputy chief engineer of the Qingdao Jiaozhou Bay Second Tunnel Project of the China Railway 14th Bureau, said that during the construction process, the tunnel passed through high-strength full-section hard rock and fault fracture zones for a long distance. The rock formation in the main line tunnel accounted for more than 80%, and the rock formation in the service tunnel accounted for more than 90%. The maximum strength reached 224 MPa, which is equivalent to 7 times the strength of ordinary concrete. The tool wear rate is high, and the tool inspection and replacement are required every 20 meters of tunneling. At the same time, the maximum seabed depth of the shield section of the main line tunnel reaches 95 meters, and the maximum seabed depth of the shield section of the service tunnel reaches 105 meters. The ultra-high seabed water pressure places extremely high requirements on shield sealing and waterproofing. In addition, hard rock excavation produces strong vibrations, which can easily cause equipment damage, slag drainage and blockage of warehouses and other industry problems. Multiple risks are superimposed, making it extremely difficult to control submarine construction.
Wang Junping, chief engineer of the Qingdao Jiaozhou Bay Second Tunnel Project of the China Railway 14th Bureau, said that the project team carried out targeted design optimization of the two shield machines. By reducing the distance between the cutters, the cutter head can be equipped with as many cutters as possible to enhance the rock-breaking ability of the shield machine. It also adopts the slag discharging system design of “screw machine + gravel box + gravel machine” for the first time in China to improve the slag discharging efficiency and reduce the risk of slag stagnation. It also innovates the shield stabilization and anti-seismic technology of the shield machine to improve the seismic resistance of the shield machine in hard rock formations and avoid abnormal damage to the cutting tools and main bearings.
In addition, in view of the difficulties in the construction of undersea tunnels, the project team also constructed a shield tail seal, simultaneous grouting water stop ring, and segment water stop waterproof system, which is equivalent to wearing three layers of “waterproof clothing” for the tunnel. Facing the box culvert assembly operation under the narrow tunnel space, for the first time in the world, the box culvert was assembled simultaneously on a small shield, realizing trackless material transportation in the tunnel, and realizing the simultaneous operation of excavation and internal prefabricated box culvert assembly.
The “Guo Signal” shield machine that completed the tunnel excavation task this time, as a “pioneer” to explore the seabed geology in advance, provided first-hand geological data, risk warning and construction reference for the main line excavation of the “Haitian”. In the later stage, the service tunnel will also assume the functions of ventilation, operation and maintenance, and emergency rescue passages. Cross passages will be set up every 1,000 meters to connect to the main tunnel. According to Chen Zongkai, shield manager of Qingdao Jiaozhou Bay Second Tunnel of the China Railway 14th Bureau, relying on digital twin technology, the project team will promptly feed back the front data collected from the service tunnel to the shield machine of the main tunnel, making the parameters of the excavation construction more precise and the control more coordinated. It also actively summarizes the law of tool wear in hard rock excavation, reduces the frequency of tool changes of the edge hob of large shields, and greatly increases the excavation distance of large shields.
Faced with the challenges of deeply buried segments, high water pressure, and high anti-seepage levels, the China Railway 14th Bureau independently developed and designed the fifth-generation ultra-large-diameter shield segment green intelligent production line and used intelligent equipment such as plastering robots, spraying robots, mold cleaning robots, and heavy-duty AGVs to achieve intelligent management of the entire life cycle of the segments and build a solid “golden bell” for the Jiaozhou Bay Second Undersea Tunnel. According to Cai Yuting, manager and party branch secretary of the Jiaodong Branch of China Railway 14th Bureau, the project is the first in the field of domestic steel fiber concrete segment construction to develop and apply a steel fiber automatic feeding device. It integrates functions such as dual metering, precise sensing, automatic data collection and transmission, and one-click automatic feeding. It effectively solves industry problems such as uneven steel fiber discharging, time-consuming feeding, and low metering accuracy. It achieves precise feeding and efficient operations, and provides a solid guarantee for the smooth production of segments.
Focusing on the engineering problems of ultra-large-diameter shield tunneling through seabed hard rock and fractured zone formations over long distances, China Railway 14th Bureau collaborated with Shandong University, Beijing University of Technology, Beijing Jiaotong University, Central South University and other universities to jointly tackle key issues, undertaking three national key projects and unveiling projects, focusing on solving problems such as abnormal tool wear, low tunneling efficiency, risk of main drive failure, and risk of shield tail breakdown. At present, 17 utility model and invention patents have been formed, 20 papers and 2 construction methods have been completed.
According to Chen Shuang, the site manager of the Qingdao Jiaozhou Bay Second Tunnel Project of the China Railway 14th Bureau, the “Haitian” shield machine of the southern main line tunnel took the lead in completing the excavation task in March this year. The dismantling work is being promoted as planned, and the overall dismantling has been completed by 50%. After the shield excavation of the service tunnel “National Signal” is completed, the disassembly and lifting construction of the shield machine will be started. The project team will summarize the experience in dismantling the super-large-diameter shield on the southern line, provide technical guidance and operational reference for the dismantling of the service tunnel shield, and ensure that the dismantling work is carried out safely and efficiently.
The Second Jiaozhou Bay Tunnel is a benchmark project for a transportation powerhouse in the new era, and was recognized by the World Tunnel Conference as one of the “50 landmark projects in the field of global tunnels and underground engineering.” After the completion of the project, it will greatly alleviate the cross-sea traffic pressure between Qingdao’s main urban area and the West Coast New District (Huangdao), significantly shorten the time and space distance, and effectively promote the integrated development of “Qingdao-Huangzhou City” and around Jiaozhou Bay.
相關鏈接
Engineering Major Events
1. In August 2022, the China Railway 14th Bureau won the bid, with a planned construction period of 52 months, and the project team rushed to the site.
2. On May 20, 2023, the “Guo Signal” mud-water balance shield machine serving the service tunnel successfully rolled off the assembly line in Nansha, Guangzhou, and the first shield machine completed factory acceptance.
3. On June 30, 2023, the “Pathfinder Pioneer” – the “National Signal” mud-water balance shield machine set off, and the service tunnel officially started subsea excavation.
4. On August 20, 2023, the “Haitian” mud-water balance shield machine serving the southern main line tunnel came off the production line and completed factory acceptance.
5. On December 30, 2023, the “Haitian” officially set off to start the excavation of the southern main line tunnel through the sea.
6. On March 26, 2026, the “Haitian” shield machine of the southern main line tunnel took the lead in completing shield excavation construction.
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